Turbine combustion fuel oils, such as JP-4, JP-5, JP-7, JP-8, Jet A, Jet A-1 and Jet B are ordinarily middle boiling distillates, such as combinations of gasoline and kerosene. Military grade JP-4, for instance, is used in military aircraft and is a blend of 65% gasoline and 35% kerosene. Military grades JP-7 and JP-8 are primarily highly refined kerosenes, as are Jet A and Jet A-1, which are used for commercial aircraft.
Turbine combustion fuel oils often contain additives such as antioxidants, metal deactivators and corrosion inhibitors. These additives are often necessary in these fuel oils to meet defined performance and storage requirements.
Turbine combustion fuel oils are used in integrated aircraft thermal management systems to cool aircraft subsystems and the engine lubricating oil. The turbine combustion fuel oil is circulated in the airframe to match heat loads with available heat sink. In current aircraft, these thermal stresses raise bulk fuel temperatures to as high as 425.degree. F. at the inlet to the mainburner fuel nozzles and above 500.degree. F. inside the fuel nozzle passages. In the augmentor or afterburner systems, skin temperatures up to 1100.degree. F. are experienced. In future aircraft, these temperatures are expected to be 100.degree. higher.
At these high temperatures (425.degree. F.-1100.degree. F.) and oxygen-rich atmospheres in aircraft and engine fuel system components, fuel degrades forming gums, varnishes, and coke deposits. These deposits plug-up the components leading to operational problems including reduced thrust and performance anomalies in the augmentor, poor spray patterns and premature failure of mainburner combustors and problems with fuel controls. Further, the engine exhaust becomes smoky and sooty and engine noise increases, both of which are undesirable characteristics for jet engines.
An economical method to inhibit and control deposit formation is to add treatment chemicals to the turbine combustion fuel oils prior to their combustion as propulsion fuels. It has been surprisingly found that deposit formation can be inhibited and existing deposits removed by the addition of a derivative of polyalkenylthiophosphonic acid to the turbine combustion fuel oils. Likewise, the formation of exhaust soot and smoke is inhibited and engine noise reduced.